Flotation of sulphide ores

ABSTRACT

Flotation of sulphide minerals from their ores is achieved by a process in which two or more conditioning steps are carried out prior to a froth flotation step. The first step comprises conditioning a pulp of the ore in the presence of at least one alkaline agent selected from a group of agents which is defined in the specification which follows. The pulp is then further conditioned in the presence of a member of the xanthate family of flotation reagents and sufficient sodium silicate to effectively disperse the host rock minerals. The resulting pulp is then subjected to froth flotation. Preferably there are three separate conditioning steps, namely conditioning carried out in the presence of (1) one of the hereinafter defined alkaline agents, (2) a member of the xanthate family of flotation reagents, and (3) sodium silicate. The invention is particularly valuable for the recovery of metallic sulphides from ores containing talcy minerals or natural slimes and the invention has been applied with signal success to the flotation of copper-nickel sulphide ores containing over 40 percent by weight of talcose host rock minerals.

United States Patent [72] inventor DavidWeston 32 Parkwood Avenue, Toronto, Ontario, Canada {21 ApplNo 727,268 [22 Filed May7,l968 [45} Patented Aug.3, 1971 [32] Priority Apr. 23, 1968 [33] Canada [31] 018,182

[54] FLO'IATION 01- SULPl-IIDE 011128 19 Claims, 1 Drawing Fig.

[52} U.S.Cl 241/16, 241/20, 209/166 [51] 1nt.Cl ..B02c 19/00, B03d1/02 [50] FieldoiSearch 209/3,5. 166,l67;241/16,20,24

[56] References Cited UNlTED STATES PATENTS 1,417,263 5/1922 Luckenbach 209/166 2,611,485 9/1952 Tveter.... 209/166 2,467,369 4/1949 Bishop 209/166. 2,693,278 11/1954 Fitzsimmons. 209/166 2,695,101 11/1954 Booth 209/166 3,094,484 6/1963 Rizo-Patron 209/166 ALKALINE AGENT ACTIVATOR werrnve AGENT XANTHATE COLLECTOR FOREIGN PATENTS Primary Examiner- Frank W. Lutter Assislant Examiner- Robert Nalper Attamey- Smart and Biggar ABSTRACT: Flotation of sulphide minerals from their ores is achieved by a process in which two or more conditioning steps are'carried outprior to a froth flotation step. The first step comprises conditioning a pulp of the ore in the presence of at least one alkaline agent selected from a group of agents which is defined in the specification which follows. The pulp is then furtherconditioned in the presence of a member of the xanthate family of flotation reagents and sufficient sodium silicate to effectively disperse the host rock minerals. The resulting pulp is then subjected to froth flotation. Preferably there are three separate conditioning steps, namely conditioning carried out in the presence of (1) one of the hereinafter defined alkaline agents, (2) a member of the xanthate family of flotation reagents, and (3) sodium silicate. The invention is particularly valuable for the recovery of metallic sulphides from ores containing talcy minerals or natural slimes and the invention has been applied with signal success to the flotation of copper-nickel sulphide ores containing over 40 percent by weight of talcose host rock minerals.

FURTHER CONDITIONING (STEP 2) FURTHER CONDITIONING (STEP 3) FLOTATION PATENTEUAUE 3m: 13,596,838

ALKALINE AGENT WET GRINDING ACTIVATOR .AND CONDITIONING WETTING AGENT (STEP I) SODIUM SILICATE AS A FURTHER DISPERSANT 8 DEPRESSANT CONDITION/N6 FROTHER E 3) FLOTATION INVENTOR DAVID WESTON -ATTORNEYS FLOTATION OF SULPHIDE ORES BACKGROUND OF THE INVENTION phide ores containing appreciable quantities of talcy-type host rock minerals. In prior flotation procedures with appreciableamounts of such host rock minerals, large quantities of the host rock are floated with the sulphides, thereby'making the operation uneconomical or resulting in low grade concen-- trates which are difficult or impossible to-upgrade and, in

many cases, poor recoveries of the sulphide values;

In addition to the abovedescribed ores, generally referred Y to as talcose ores, this inventionris especially useful for the recovery of sulphides from a broad field of host rock materials 1 such as those contained in mud seams, graphite, andores with natural slime: that interfere generally in the same manner in the flotation of sulphide ores containing talcose-type minerals.-

In the past, the method of treating such ores has been either to deslime the pulp before flotation resulting in major sulphide value losses, or a prefloat made ahead of the sulphide float also resulting in major sulphide losses, or where the ore is of sufficiently high grade the deleterious material is floated with the sulphides resulting in a low grade concentrate being shipped to the smelter, or alternately, cleaned many times, resulting in a medium grade concentrate with comparatively low value recoveries.

BRIEF SUMMARY OF "rue mvemiou I have invented a process wherein the sulphides can be With my process there is no need to deslime prior to the sul phide flotation, or make an initial prefloatfor discardingto tailingsor further treatment.

As will be seen from the following, my process may involve unusual combinations of reagents together with preconditioning steps wherein the reagents added in each step and their concentrations are major factors in this surprisingly effective 1 flotation procedure. It will also be'seen in the following that selection of alkaline agents is most important and optimum results are only obtainable with agents. I 1

My invention maybe generally defined as a process for the flotation recovery ofat least one sulphide mineral from an ore of the same by a process in which at least two stages-of conch-- "correct combinations of tioning precede flotation, said process comprising conditiom ing a pulp of the ore in the presence of an alkaline agent selected from the group consisting of alkali metal carbonates, ammonium hydroxide, mixturesof these compounds, and mix- 'tures comprising at least one of the compounds and at least one hydroxide selected from the group co'nsist-ingl of sodium, potassium and calcium hydroxides; and, in the presence of a member of the xanthate family of flotation reagents and a-sufficient amount of sodium silicate to maintain the host minerals effectively dispersed, further conditioning the said pulp and subjecting same to froth flotation;

The presently preferred process according to the invention includes three conditioning steps. in thefirst conditioning step the ore, together with activating agents or wetting agents which are to be used, is conditioned in thepresence of an alkaline agent which maybe either an alkali metal carbonate or ammonium hydroxide, or mixtures'of these "compo'unr'ls, or

mixtures of one or both of thesecompounds with a hydro'xide 1 selected from the group consisting of sodium, potassium and calcium hydroxide. This conditioning 'step is carried outil'ora period of time sufficient to activate the mineral and with sufficient alkaline agent to bring the pH ofth'e resulting pulp to a point within the optimum range for flotation of the desired mineral. The pulp resulting from this TITS! step is now subjected 'to a second conditioning-step in the presence of a selected memberof the family of xanthate flotation reagents for a time predetermined by experiment to produce maximum activation; The third conditioning step comprises conditioning the pulp resulting from the second step in the presence of sodi- 'um silicate once again in an'amount and for a time predetertion required afler the stages of preconditioning iscomparatively short as compared to conventional flotation circuits, even as compared with those which are free of such deleterious material. This not only means anappreciable saving in capital cost but also a possible reduction in operating costs. Following the addition of the frother I found that the sulphides float in the roughercircuit extremely rapidly using a rougher flotation time of 7 to 12 minutes. The normal rougher flotation time in the flotation of the nickel mineral pentlandite in current conventional circuits is 45 'minutes.

The data from this invention also'indicates that it may be applied for additional host rock rejection to current base metal sulphide flotation plants to reduce the insol in the final concentrates now being produced from ores containing the normal host rock materials and that have heretofore not been considered troublesome'By reducing the insol in the concentrates both freight and smelter costs will be reduced.

In the detailed description which follows, I have shown that excellent results may be obtained on a copper-nickel sulphide ore using as one combination, sodium carbonate and ammonium hydroxide as the alkaline controlling reagents in the process. in the application of this process, it may well be found that on other types of ores containing different host rock constituents or-other sulphides such as lead and zinc, other alkaline combinations may either be more economical or show improved results over the sodium carbonate-ammonium hydroxide circuit found best for this copper nickel ore. With this copper nickel o're I have found it advantageous to use copper sulphate as an activator in the initial conditioning step, whilst with a sulphide such as g-alena no such activating agent is required.

When theconventional xanthate flotation method for flotation of this ore is used, the inventor was informed that the maximum grade of concentrate producible was in the range of 2-2Vz percent nickel with recovers of approximately 65-70 percent. Wit'hmy process a concentrate grade in excess of 5 percent nickel was produced with final recoveries indicated in excessof percent. In my'.process i not only found that the preconditioning stages'were important, but also the method in which I carried o'utmy cleaning. Again, a shortconditioning stage with the additi'on-of reagents before each cleaner gave optimum results.

BRIEF DESCRIPTION OF DRAWlNG A drawing is attached which is a flowsheet of the preferred embodiment of the invention.

DETAILED DESCRIPTION Referring to the drawing, in this preferred procedure which is applied to the flotation of copper and nickel sulphides from its ore, the wet grinding and first-conditioning step are carried outsim'ultaneously, theore being fed to'a wet-grinding system -'"to'gether with awetting agent, at least one alkaline reagent,

vention is set out in example I which follows. The ore treated 5 in example I was a copper-nickel sulphide ore containing an estimated average 40 percent of talcose-type. minerals. The sample contained 0.52 percent nickel in the form of pentlandite and 0.025 percent copper in the form of chalcopyrite.

bonate in combination with lime alone and sodium carbonate in combination with sodium hydroxide. Because of the similar chemical properties of sodium hydroxide and potassium hydroxide, it is apparent that potassium hydroxide could be substituted for sodium hydroxide in the combinations above where sodium hydroxide gave beneficial results. I have set out below in tabular form the results of a series of tests using various alkaline reagents, the conditions in each case being exactly the'same as described in example 1 except for the in- The ore was ground in a laboratory rod mill at 60 percentv'dieeted ehangesin the alkaline g P solids to a fineness of about 95 percent minus 200 mesh in the The test numbers are shown in the first column of this table TABLE I Table Showing Effect 01 Use of Difi'erent Alkaline Reagents Alkalis used, lbs/ton Rougher tailings pH Test step Percent Percent Percent 3 Nil-2603 NH4OII Ca(OH)-; NaOII wt. Ni Cu presence of the equivalents of 7.5 pounds per ton of ore of a nd te st No. 204 is the test which gave the results fully set out sodium carbonate, 0.62 pounds per ton of ore of ammonium above in example I. hy p n s p r n f r f ac i ator (copper It is immediately apparent from a study of table I that the sulphate) and 0.075 pounds per ton of ore of a wetting agent results obtained with calcium hydroxide alone, sodium which was a trimethyl nonyl ether of polyethylene glycol. The hydroxide alone or a combination of these two components grinding time was 40 minutes during which period the first gave inferior metallurgical results. Throughout this table the condiliming p was eemli'leledv The resulting P p was illustrations shown represent the best metallurgy that was atsubjected to a second conditioning step for a period of 20 tained in o timizing such reagent or reagent balances. minutes with the addition of 0.l25 pounds per ton of potassi- Reference will ow be made to the manner in which one um amyl xanthate- The pulp esulting fro the se ondmay predetermine the optimum conditioning periods. To artioning step was subjected to a third-conditioning ep o a rive at the optimum period for conditioning during step i, one period of 10 minutes in the presenc f 35 p un d um runs a series of tests, the first being taken immediately at the icate per ton of ore. At the end of the econd st p h lend of grinding and further tests at intervals ofa few minutes p e Showed heavy floeulatio" Surface of the p p- 40 up to an hour of conditioning subsequent to completion of Following the addition of sodium s1l1cate in the third step, the grinding, If no economic improvement is shown by additional host rock as heavi y dispers h l th p i e flOCS nly conditioning after grinding, one would, of course, immediately partially broke up. At the end of approxlmately l mtnute folproceed with conditioning step 2 but if improvement is reallowing the addltlon of Sod um ili at th p i flOCS ized with further conditioning, the cutoff point in time will be strongly reformed while the host rock mtnerals remained a factor f he in ea ed mineral recovery vs. the cost of heavily dispersed. The pH of the pulp at the end of the thirdconditioning step was 9.8. During the last 2 minutes of this conditioning stage, frother was added which was two drops of pine oil. The resulting pulp was then subjected to froth flotation for a period of l2 minutes during which 0.05 pounds per ton of xanthate was added and two additional drops of pine oil. The pulp temperature was 36 C.

The rougher tailings amounted to 75.6 percent by weight and were remarkably low in nickel content. The nickel analysis was 0.097 percent while the copper analysis was 0.0 l 8 per cent. So far as I am aware, it has never in the past been possible to obtain results of this order in the case of an ore having a talcose content of this magnitude.

While in the preferred process described in detail above all of the first conditioning step is completed during wet grinding it should be appreciated that the first step might be carried out partially during wet grinding, with the remainder of this firstv conditioning step being conducted after the grinding has been completed. Furthermore, in certain cases it may be desirable to carry out the entire first-conditioning step after either wet or dry grinding.

As indicated above, other alkaline reagents may be employed but experiments I made with the conventional alkaline reagent used in the flotation of copper and nickel sulphides namely lime, gave poor recoveries and had a tendency to float an appreciable percentage of the host rock. The use of sodium hydroxide by itself also gave unsatisfactory results. I was, however, able to obtain satisfactory results with, in addition to the combination mentioned in example 1, sodium carbonate by itself, ammonium hydroxide by itself, sodium carbonate and ammonium hydroxide in combination with lime, sodium car-' further conditioning. This may be illustrated by comparing the results which were obtained with tests and 162 which will now be described as examples ll and II] respectively.

EXAMPLE ll Test 150 The wetting agent, sodium carbonate, ammonium hydroxide and copper sulphate were added to the grinding circuit at the rates of 0.075, 7.5, 0.62 and 0.45 lbs. per ton respectively. Step I took place simultaneously with the grinding and step 2 was a 7 minute conditioning cycle with 0.125 lbs. per ton of potassium amyl xanthate (Z6) added. In step 3, 35 lbs. per ton of sodium'silicate was added and the conditioning time was 10 minutes. The frother was pine oil and during rougher flotation 0.05 lbs. per ton of Z6 was added.

"The rougher tailings were 80.1 percent by weight and analyzed 0. l 01 percent nickel.

EXAMPLE lll Test 162 This test is a near duplicate of test 150 with the exception that step I included a 45 minute conditioning period following the grinding stage. All other conditions were the same with the exception that slightly less wetting agent was used, namely 0.0625 lbs. per ton.

The rougher tailings were 79.8 percent by weight analyzing 0.097 percent nickel. r-

In comparing this test to test 150 the inclusion of additional conditioning following grinding and before'the xanthate conditioning indicates a slightly higher recovery but may not be economically justified.

ple of ore.

TABLE II Conditioning time, mins. Rougher tailings Text Step Step Percent Percent Percent .\'o. Step 1' 2 3 wt. Ni Cu '5 10 T3. 2 0.113 0. 019 2 1 Grinding cycle 2. 5 T7. 4 0. 110 0. 018 onl through- 5.0 10 77. J 0.109 0. 010 203. out tests. 10. O 10 T5. 6 0. 101 0. 018 204. 20. 0 10 75. 6 0 007 0.018

The major break in the tailings losstakes place between 5 and 10 minutes conditioning time and shows a furthersmall in- EXAMPLE IV In the following'comparative tests I20 and 123, all reagents v and conditioning periods were. the same with the exception thatin test 120, 37".: pounds per ton of sodium silicate was used as against pounds of sodium silicate per ton of ore in I test l23. It was found that in test I23 the sodium silicate concentration had dropped below the lower effective concentration of the dispersant for optimum metallurgicalresults. ln test 120; thepercentage weight of the ore rejected in the tailings was 78.1, analyzing 0.130 percent nickel, as against the lower tailings rejection in test 123, that is 74.7 percent by weight analyzing0.l44-percent nickel. It is obvious that the percentage of material floating suffered and that there was a higher nickel loss in the tailings when the sodium silicate concentration is lower than that required to effectivelydisperse and depress the host rock minerals. 1

While I generally prefer to add all the dispersantduring the third-conditioning step, i have found it possible to add a minor part in step '1 and the major part in step 3. Results obtained from adding a portion of the2dispersant during this first step are shown in table iV.

' TABLE IV N azSiOa,

lbsJton Conditioning time, mms. Rougher tailings Test Step Step Step Step Percent Percent Percent No. 1 3 Step 1* 2 3 wt. Ni u Grinding cycle 20 10 75. 6 0. 097 0. 018 25 only through- 20 10 74. 6 0. 098 0. 018 17. 5 out tests. 20 10 75. 0 0. 103 0. 019

crease in recovery at 20 minutes. Optimum condition time for step 2 is seen to be between about l0to SO-minutes.

The time period of the third-conditioning step is similarly predetermined by experimentation and a group of such-ex? 35 periments are illustrated in table lll describing four tests in which the only variable is the period allotted to the third-conditioning step.

TABLE III Conditioning time, ruins.

it will be noted that the tailings loss increases between l0 and 20 minutes conditioning withno noteworthy difi'erences .in metallurgy between 2 and lO minutes. It may be seen from this table that the'third-conditioning step for optimum-results should not be carried on for more than l0 minutes and the preferred period is some 2%: to 5 minutes. It will also :be'noted that at 20 minutes metallurgy suffers. In thiscycle it is therefore important not to exceed the selected timeperiod by::an appreciable time.

The amount of sodium silicate whichshould-be present during the third conditioning step must also,-.in the case of each ore, be predetermined by experiments. On an .ore of this-type with high talcose content using conventional flotation means well known to the art, the mass of the ore tends to float producing a very low grade concentrate. To .obtain-theoptimum amount of sodium silicate required *to substantially disperseand depress the host rock minerals, lkeep increasing the amount of sodium silicate until acomparatively-cleandife 5 ferential sulphide float is obtained. .i then continue with a slight excess over this amount and then conducta series=of controlled tests using lesser amounts until thehost :rock :againbegins to interfere with the float and-the amount of sulphide mineral in the tailings increases. The optimumrangeof sodium silicate concentrate is now indicated. The following-are two comparative tests showing the lower end of the-:range compared to the optimum concentration of sodium silicate which is approximately 25 percent higher than the lower'limit tested.

Roughcr tailings 40 In tables -ll, Ill and IV the step i conditioningcycle coincides with the time of grinding. No additional conditioning has been done subsequent to grinding.

In comparing the results of these tests to 204 wherein all of the dispersant was added to step 3, as against approximately 30 percent to the grinding circuit with'70 percent to step 3 .(test 209'), the results, although slightly poorer, maybe considered a standoff.

With SOpercent-(test 217) of the dispersant added to the grinding circuit :and "50 percent to step 3, there is a noticeable increase in tailings loss of nickel. Froman operational point of view where it may be desirable to circulate part of the recovered solution vfrom the flotation circuit tailings to the grinding circuit, and'wherein there will be a number of the reagents including sodium silicate partially recovered, this characteristic of the circuit in being able to tolerate somewhat in excess of 30Lpercent of the total sodium silicate required without undue nickel loss can be important economically'in reduction in theoverall reagent cost as shown in this open circuit.work..

The'efiectof reversing thetimes of addition of the sodium silicate dispersant and the xanthate collector is illustrated in table V in which the sodium silicate is added during step 2, and thexanthate in step v3.

TABLE V Conditioning time, mins. Rougher tailings Percent Percent Percent Test No.' Step'l Step 2 Step 3 wt. Ni Cu \Vhenthe results of these three'tests are compared with the :results-obtained'in test 204 as set out in table'IlLit will im- EXAM PLE Vl This.example,-=whiclrincludesadescription of rougher concentrate 'cleaning, was .carriedouton an ore sample taken from :the'same'orebody as thesamples used in the preceding examples. This sample,'however, :had a :higher percentage of talc, probably exceeding 50 percent, and was the most refractory to flotation treatment.

Reagents added during grinding 0.075 lbs. per ton wetting agent 0.45 lbs. per ton CuSO 0.62 lbs. per ton r\'H,OH

8.75 lbs. per ton Na.,CO,

Step lthe grinding time plus 15 minutes of further conditioning.

Step 2-0. I 25 lbs. per ton potassium amyl xanthate, minutes conditioning Step 340 lbs. per ton Na Sio minutes conditioning, 2

drops pine oil last 2 minutes of conditioning F loatl 2 minutes with addition of 0.05 lbs. per ton potassium amyl xanthate and one drop of pine oil.

The rougher concentrate was conditioned for 5 minutes with the following reagents added:

Wetting agent-0.012 lbs. per ton Potassium amyl xanthate-0.025 lbs. per ton NH,OH0.25 lbs. per ton Na SiO, l .5 lbs. per ton The number l cleaner concentrate was conditioned for 5 minutes with the following reagents added:

NH OH0.25 lbs. per ton It will be noted that the concentrate grade produced in two cleaners only was in excess of 5 percent nickel with the total cleaner tailings analyzing 0.38 percent nickel as against a head value of0.52 percent nickel.

At a grade of approximately 5 percent nickel, analysis of the concentrate showed an insol content of approximately 13 percent which is considered excellent in the case of such ores.

I claim:

l. A process for the flotation recovery of copper and nickel sulphide minerals from ores containing both such minerals by a process in which at least two-conditioning steps precede flotation, said process consisting essentially of; conditioning a pulp of the ore in the presence of at least one alkaline agent selected from the group consisting of alkali metal carbonates, ammonium hydroxide, mixtures of these compounds, and mixtures comprising at least one of the compounds and at least one hydroxide selected from the group consisting of sodium, potassium and calcium hydroxides; and then adding a member of the xanthate family of flotation agents to activate the. said minerals and conditioning the xanthate activated pulp in the presence of a sufficient amount of sodium silicate to maintain the host rock minerals effectively dispersed; and then subjecting the thus conditioned pulp to froth flotation.

2. A process as defined in claim 1, in which the sodium silicate is present in a minimum amount equivalent to about 30 pounds of sodium silicate per ton of sol-ids in said pulp up to an said minerals; then (0) a third conditioning step wherein the amount where further quantities show no further beneficial effeet.

3. A process as defined in claim 1, in which'the first-conditioning step is at least partially carried out during one or more wet-grinding stages. 1

4. A process as defined in claim 1, in which the entire firstconditioning step is carried out subsequently to one or more wet-grinding stages.

5. A process as defined in claim 1, in which the alkaline agent is sodium carbonate.

6. A process as defined in claim 1, in which the alkaline agent is ammonium hydroxide.

7. A process as defined in claim 1, in which the alkaline agents are sodium carbonate and ammonium hydroxide.

8. A process as defined in claim l, in which the alkaline agents are sodium carbonate, ammonium hydroxide and calcium hydroxide.

9. A process as defined in claim 1, in which the alkaline sulphate is added as an activating agent during said first-conditioning step.

12. A process as defined in claim 1, in which a trimethyl nonyl ether of polyethylene glycol is added as a wetting agent during said first conditioning step.

13. A process as defined in claim 1, in which the xanthate reagent employed is sodium amyl xanthate.

14. A process as defined in claim 1, in which the xanthate reagent employed is potassium amyl xanthate.

15. A process for the flotation recovery of copper and nickel sulphide minerals from ores containing both such minerals by a process in which at least two-conditioning steps precede flotation, said process consisting essentially of (a) a first-conditioning step wherein the ore, together with such activating agents and wetting agents as are to be used, is conditioned in the presence of at least one alkaline agent selected from the group consisting of alkali metal carbonates. ammonium hydroxide, mixtures of these two compounds, and mixtures comprising at least one of these compounds and at least one hydroxide selected from the group consisting of sodium potassium, and calcium hydroxides, in an amount calculated to bring the pH of the resulting pulp up to a point within the optimum range of flotation of the said minerals, for a period of time sufficient to activate said minerals, then (b) a secondconditioning step wherein the pulp resulting from the first step is conditioned in the presence of a selected member of the family of xanthate flotation reagents for a period of time determined by experiment to produce maximum activation of pulp resulting from the second step is conditioned in the presence of sodium silicate in an amount and for a time, predetermined by experiment, to be sufficient to effectively disperse the host rock minerals; and then (d) subjecting the resulting pulp to froth flotation.

16. A process as defined in claim 15, in which the secondconditioning step is carried out for a period of from 10 to about 30 minutes.

17. A process as defined in claim 15, in which the third-conditioning step is carried out for a period of less than 10 minutes.

18. A process as defined in claim 15, in which the secondconditioning step is carried out for a period of from about 10 to about 30 minutes, and in which the third-conditioning step is carried out for a period of less than 10 minutes.

19. A process as defined in claim 15, in which the sodium silicate is added as dispersant during both the first and thirdconditioning steps, the amount added in the first step being less than that added in the third step. F 

2. A process as defined in claim 1, in which the sodium silicate is present in a minimum amount equivalent to about 30 pounds of sodium silicate per ton of solids in said pulp up to an amount where further quantities show no further beneficial effect.
 3. A process as defined in claim 1, in which the first-conditioning step is at least partially carried out during one or more wet-grinding stages.
 4. A process as defined in claim 1, in which the entire first-conditioning step is carried out subsequently to one or more wet-grinding stages.
 5. A process as defined in claim 1, in which the alkaline agent is sodium carbonate.
 6. A process as defined in claim 1, in which the alkaline agent is ammonium hydroxide.
 7. A process as defined in claim 1, in which the alkaline agents are sodium carbonate and ammonium hydroxide.
 8. A process as defined in claim 1, in which the alkaline agents are sodium carbonate, ammonium hydroxide and calcium hydroxide.
 9. A process as defined in claim 1, in which the alkaline agents are sodium carbonate and sodium hydroxide.
 10. A process as defined in claim 1, in which the alkaline agents are sodium carbonate and calcium hydroxide.
 11. A process as defined in claim 1, in which copper sulphate is added as an activating agent during said first-conditioning step.
 12. A process as defined in claim 1, in which a trimethyl nonyl ether of polyethylene glycol is added as a wetting agent during said first conditioning step.
 13. A process as defined in claim 1, in which the xanthate reagent employed is sodium amyl xanthate.
 14. A process as defined in claim 1, in which the xanthate reagent employed is potassium amyl xanthate.
 15. A process for the flotation recovery of copper and nickel sulphide minerals from ores containing both such minerals by a process in which at least two-conditioning steps precede flotation, said process consisting essentially of (a) a first-conditioning step wherein the ore, together with such activating agents and wetting agents as are to Be used, is conditioned in the presence of at least one alkaline agent selected from the group consisting of alkali metal carbonates, ammonium hydroxide, mixtures of these two compounds, and mixtures comprising at least one of these compounds and at least one hydroxide selected from the group consisting of sodium potassium, and calcium hydroxides, in an amount calculated to bring the pH of the resulting pulp up to a point within the optimum range of flotation of the said minerals, for a period of time sufficient to activate said minerals, then (b) a second-conditioning step wherein the pulp resulting from the first step is conditioned in the presence of a selected member of the family of xanthate flotation reagents for a period of time determined by experiment to produce maximum activation of said minerals; then (c) a third conditioning step wherein the pulp resulting from the second step is conditioned in the presence of sodium silicate in an amount and for a time, predetermined by experiment, to be sufficient to effectively disperse the host rock minerals; and then (d) subjecting the resulting pulp to froth flotation.
 16. A process as defined in claim 15, in which the second-conditioning step is carried out for a period of from 10 to about 30 minutes.
 17. A process as defined in claim 15, in which the third-conditioning step is carried out for a period of less than 10 minutes.
 18. A process as defined in claim 15, in which the second-conditioning step is carried out for a period of from about 10 to about 30 minutes, and in which the third-conditioning step is carried out for a period of less than 10 minutes.
 19. A process as defined in claim 15, in which the sodium silicate is added as dispersant during both the first and third-conditioning steps, the amount added in the first step being less than that added in the third step. 